The present application relates to a rotary wing aircraft main rotor blade spar.
Conventional rotary wing aircraft rotor blades include a spar that functions as the primary structural member of the rotor blade to react torsional, bending, shear, and centrifugal loads. A leading edge and trailing edge assembly envelop the spar to yield a desired airfoil contour. The spar typically extends along the length of the rotor blade and mounts at an inboard end to a cuff assembly that mounts to a rotor hub.
The spar is often manufactured of a high strength metallic material such as a titanium alloy. The spar is a relatively expensive component that is often retrieved from a damaged or worn main rotor blade such that a remanufactured main rotor blade may thereby be assembled with the refurbished spar.
Spar retrieval is conventionally accomplished through heat decomposition and manual chiseling and scraping of main rotor blade components therefrom. Remnants of the main rotor blade components, oxidized coatings, adhesives and primer are conventionally stripped from the spar by a heated caustic solution. Moreover, the spar may have one or more areas that are below a minimum specified thickness such that the particular areas are built up with a metallic deposit. The spar is then heat treated to relieve residual stresses. The result is an alpha-embrittled zone of oxygen-enriched alpha phase that is generally termed an “Alpha-case”. The Alpha-case may be deleterious to the subsequent use of the spar because of the resultant reduced ductility and fatigue resistance as compared with the underlying alpha-beta or other microstructure.
The current practice of Alpha-case removal involves hydrofluoric acid etch and hand grinding which are relatively labor intensive and may generate undesirable fumes.